The problem here is all about corrosion. If a steel stud corrodes with the ally head (dis-similiar metals), they will seize solid. This though is not a problem since the stud stay where it is and the nut comes off it (the nut also being steel shouldn't react with the steel stud).
If you use steel bolts however, then when they seize to the head, you'll a) round the heads off b) shear the heads off d) shear the bolt off, leaving the base in the head, or e) strip the threads in the head.
Any of these are a real pain in the butt, and can junk your head.
You might be able to get away with it if a) you use really good high-temp anti-seize compound (contact an aerospace supplier to the really good toad), and are careful when torquing them, or b) you rarely use the bike (ie trackdays, race meets), and are happy to remove and grease the bolts on a regular basis to prevent corrosion building up.
You could try good quality thread inserts, like helicoils or the solid alternative. I think MM posted something on here about them. But do you really want to risk junking you head?
FYI,
I'm planning on using very good quality stainless bolts myself, along with high-temp anti-seize, when I rebuild my zxr cafe racer. But it's going to be naked, and be having an under seat radiator and oil cooler, so I can check the bolts very easily. Not so easy on a fair bike!
